A variety of curable resin compositions are known in the coating industry including those comprising hydroxyl group-containing acrylic or polyester polymers and a crosslinker such as melamine resins or organic polyisocyanates. The melamine resin-crosslinking compositions suffer not only from volumetric shrinkage upon curing due to the emanation of lower alkanol by-products but also from a decreased weatherability particularly when exposed to acid rain, due to the presence of triazine nuclei. The polyisocyanate crosslinking system has problems of toxicity, decreasing weatherability with time and yellowing.
Japanese Laid Open (Kokai) Patent Application Nos. 36109/82 and 155660/83 disclose a system having an enhanced weatherability comprising room temperature-curable alkoxysilyl group-bearing acrylic polymers. This system has certain defects in that the curing reaction proceeds slowly, that the cured product can be blotted with by-products produced by the hydrolysis of residual alkoxysilyl groups and that its rust prevention property is not satisfactory.
Japanese Patent Publication (Kokoku) No. 33152/88 discloses a thermosetting resin system utilizing a reaction between an alkoxysilyl component and a hydroxyl group-containing resin component. This system is also disadvantageous in that its curing reaction proceeds slowly and the resulting cured film exhibits poor salt spray resistance.
It has long been known in the art to crosslink vinylpolysiloxanes with organohydrogenpolysiloxanes in the presence of a platinum catalyst. Unfortunately, the cured product of this composition is swellable with conventional organic solvents and thus exhibits poor solvent resistance as well as poor alkali resistance. This composition also has a poor overlaying property when used for coating purposes. These defects have precluded the composition from its application to coating compositions of general use.
In addition, the above hydrosilyl reaction by the organohydrogenpolysiloxanes has been utilized to obtain rubbery resilient products by reacting the organohydrogenpolysiloxanes with alkenyl group-bearing polymers or oligomers in the presence of a hydrosilylation catalyst such as chloroplatinic acid. See, Japanese Laid Open Patent Application Nos. 138230/89, 95266/82, 200807/82 and 277645/82.
All of the above compositions are reactive even at room temperature and, therefore, at least the catalyst must be kept separately from the remainder of the compositions immediately prior to use. Moreover, rubbery products are not suitable for coating purposes in which mechanical strength is a requisite for the coating films. Organohydrogenpolysiloxane components used in known compositions generally exhibit a poor compatibility with alkenyl group-containing polymers or oligomers which also contributes to decreased mechanical strength of the resulting coating films.
It is, therefore, a principal object of the present invention to provide a curable resin composition utilizing a hydrosilylation reaction of an alkenyl group as the curing mechanism thereof in which the hydrosilating component and the alkenyl group-containing component are readily compatible with each other.
It is another object of this invention to provide a curable resin composition which has excellent mechanical strength, weatherability, acid resistance, alkali resistance, waterproofness, salt spray resistance, solvent resistance, overlaying property and other properties.
It is a further object of this invention to provide a curable resin composition which is curable without volumetric shrinkage and thus may be used for molding purposes.
It is a still further object of this invention to provide a curable resin composition which may be used for coating purposes as solventless or high solids coating compositions.